Problem: Simplify the following expression: $z = \dfrac{n^2 + 7n - 30}{n - 3} $
Explanation: First factor the polynomial in the numerator. $ n^2 + 7n - 30 = (n - 3)(n + 10) $ So we can rewrite the expression as: $z = \dfrac{(n - 3)(n + 10)}{n - 3} $ We can divide the numerator and denominator by $(n - 3)$ on condition that $n \neq 3$ Therefore $z = n + 10; n \neq 3$